240v - 5vdc ultra low power

[Scolly]

what im putting together is a 2.4ghz wireless transmitter/reciever using these units
**broken link removed**

these guys only need 55mA at 5v and i cant really see the point in paying $15 each for a pair of plug in power supplies that can supply 1 amp

what i want to know is what would be the cheapest way to make a pair of power supplies able to deliver 100mA at 5v the output need not be very clean as it will be going through a +5v regulator ic

 

[3v0]

what im putting together is a 2.4ghz wireless transmitter/reciever using these units
**broken link removed**

these guys only need 55mA at 5v and i cant really see the point in paying $15 each for a pair of plug in power supplies that can supply 1 amp

what i want to know is what would be the cheapest way to make a pair of power supplies able to deliver 100mA at 5v the output need not be very clean as it will be going through a +5v regulator ic

How about a non engineering solution.

If you do not intend to go into production, you should be able to get the wall warts at a local second-hand/thrift-store. I pay between 25 and 50 cents each.

Unless you are using low dropout regulators you should look for a 9V PS. 7.5V can work, 12V can overheat the regulators. YMMV

 

[justDIY]

55mA is hardly ultra low power! If you needed 1uA to 1ma, a shunt regulator would be a good fit.

like 3v0 points out, a second hand or surplus wall wart is your best bet for cheap power

 

[evandude]

Agreed, there's little to no chance you could build your own power supply for less than the cost of a cheap wallwart. If you tried to build a transformer-based supply you'd just be doing exactly what the wallwart does, and if you tried to build a switching supply you'd end up doing a ton of work. And either way, the components would surely cost more than a wallwart, not even counting the time and effort involved.

 

[mvs sarma]

what im putting together is a 2.4ghz wireless transmitter/reciever using these units
**broken link removed**

these guys only need 55mA at 5v and i cant really see the point in paying $15 each for a pair of plug in power supplies that can supply 1 amp

what i want to know is what would be the cheapest way to make a pair of power supplies able to deliver 100mA at 5v the output need not be very clean as it will be going through a +5v regulator ic

WHY NOT USE A CELL CHARGER LIKE NOKIA TYPE. IT CAN GIVE 5v dC AT atlest 200mA

 

[Sceadwian]

Cell phone chargers are a real steel nowdays. A lot of them are switchers so are both very small and relatively high current, and since cell phones are upgraded as frequently as they are now, always in high supply at thrift shops or surplus stores.

 

[Hero999]

Lots of them aren't real switchers though because they aren't regulated; they basically crappy wallwarts running at a higher frequency and the ripple is probably terrible. I've opened one up once and it was just a transistor oscillator on the mains side with a rectifier, small filtering capacitor and resistor (to provide a minimum load) on the secondary side. The primary and secondary sides were on separate little PCBs and there was no feedback whatsoever. Even though it was rated at 5V the output measured about 8V off load.

 

[mvs sarma]

Lots of them aren't real switchers though because they aren't regulated; they basically crappy wallwarts running at a higher frequency and the ripple is probably terrible. I've opened one up once and it was just a transistor oscillator on the mains side with a rectifier, small filtering capacitor and resistor (to provide a minimum load) on the secondary side. The primary and secondary sides were on separate little PCBs and there was no feedback whatsoever. Even though it was rated at 5V the output measured about 8V off load.

YES, I TOO HAVE SEEN SUCH ITEMS. Not every items suits our requirement. We have to check the voltage on opencircuit and then adopt selected items.